The present invention relates to a pneumatic tire, in which an inner liner is eliminated to reduce the tire weight, whereas the steering stability, ride comfort, durability and the like can be improved.
In pneumatic tires used without a tube, the inside of the tire is covered with an inner liner made of air-impermeable butyl rubber compound disposed on the inside of a carcass.
The laid-open Japanese patent application Nos. JP-A-6-156007 and JP-A-8-113007 disclose tubeless tires, wherein a butyl rubber compound is used for a topping rubber of a carcass, and an inner liner is eliminated to reduce the tire weight. As the butyl rubber is low in the impact resilience in comparison with diene rubber usually used as topping rubber, when the butil rubber is used as carcass topping rubber, the steering stability, ride comfort and the like are liable to deteriorate.
An object of the present invention is therefore to provide a tubeless tire, in which a butil rubber compound is used as carcass topping rubber, whereas the steering stability and ride comfort can be improved.
Further, when the butyl rubber is used as carcass topping rubber, a separation failure is liable to occur at the carcass ply turnup end if a stress concentration occurs.
Another object of the present invention is to provide a tubeless tire, in which a butil rubber compound is used as carcass topping rubber, whereas a separation failure is prevented to improve the durability.
According to the present invention, a pneumatic tire comprises
a tread portion,
a pair of sidewall portions,
a pair of bead portions with a bead core therein,
a carcass ply extending between the bead portions and including a topping rubber layer,
the topping rubber layer facing the inside of the tire and made of a butyl rubber compound containing at least 10 parts by weight of butyl rubber or butyl rubber derivative,
a thickness of the butyl rubber compound measured between the inner surface of the tire and adjacent cords of the carcass ply being in the range of 0.2 to 1.0 mm,
a belt disposed radially outside the carcass in the tread portion,
the belt comprising at least one ply of monofilament cords laid at an angle of from 10 to 40 degrees with respect to the circumferential direction of the tire, and
each of the monofilament cords consisting of a single filament.
Preferably, the carcass ply is turned up around the bead core in each bead portion so as to form a pair of turnup portions and a main portion therebetween, and a bead apex made of hard rubber is disposed between the turnup portion and main portion. The height of the bead apex is decreased into the range of 10 to 20 mm, and the turnup portion adjoins the main portion above the bead apex.